1. Field of the Invention
This invention relates to a device for adjusting the height of a cushion in the rear part of the seat such as a seat cushion mainly for a vehicle and, more particularly, to an improvement in a device for adjusting the height of a cushion in the rear part of the seat of an automotive seat.
2. Description of the Prior Art
In a conventional device for adjusting the height of a seat cushion of a seat for a vehicle, a rod 1 is, as shown in FIGS. 1 and 2, disposed from the front part to the rear part of the seat, the rod 1 is rotatably supported to a stationary member 4, to which the seat is pivotally secured, such as an upper raised portion of a seat track through a front bracket 2 and a link 3, a movable element 6 is engaged with the threaded part 5 formed on the rear end of the rod 1, and the link 3 and a supporting bar 7 are rotatably secured to the movable element 6.
On the other hand, to a rear bracket 8 fixed to the stationary member 4 is rotatably supported a shaft 9, the link 3 is fixed substantially at the central part to the shaft 9, and the bar 7 is also fixed to the shaft 9.
The link 3 is formed substantially in an L shape, is rotatably secured at its one end to the movable element 6 and is rotatably secured at the other end to a frame 10 at the rear part of the seat via a pin 11. Therefore, when the rod 1 is rotated forwardly or reversely by a handle H, the element 6 which is restricted in rotation by the link 3 and the bar 7 is moved under the guidance of the threaded part 5 in a direction designated by an arrow A or B.
Movement of the movable element 6 in a direction designated by the arrow A causes the pin 11 portion of the link 3 to rock in a direction designated by an arrow C, and the rear part of the seat cushion is accordingly raised through the frame 10. The movement of the element 6 in a direction designated by the arrow B, on the other hand, causes the pin 11 portion of the link 3 to rock in a direction designated by an arrow D, and the rear part of the seat cushion is consequently lowered through the frame 10. In this arrangement, stoppers 12 and 13 are defined to respectively specify the moving unit of the element 6 in the directions denoted by the arrows A and B.
With the above-described structure, the rear part of the seat cushion can be elevationally adjusted in the height. However, a large force is not only required to move the movable element 6 by rotating the rod 1 and hence by rotating the threaded part 5 of the rod 1 merely with this structure, but the seat cushion is fluctuated due to the displacement of the rod 1 caused by the backlash of the threaded part 5 of the rod 1 when an occupant sits on the seat cushion, thereby causing a drawback of a deterioration in the occupant's sitting feeling on the seat cushion.